Selenium is a trace mineral that is incorporated into proteins to form selenoproteins. Some selenoproteins act as antioxidant enzymes that help prevent free radical damage to cells. Free radicals are by-products of oxygen metabolism that may contribute to chronic diseases like cancer and heart disease. Other selenoproteins regulate thyroid function and assist in immune function. The recommended daily allowance for adults is 70 μg selenium daily. Meats, seafood, wheat products, rice, oats, eggs and some nuts are good sources of selenium. Selenium supplementation has been used to prevent or treat many conditions but studies have had conflicting results.
Selenium and Cancer
According to the Office of Dietary Supplements, observational studies show that death from lung, colorectal and prostate cancers is lower in people with higher selenium intake. It is believed that selenium may affect cancer by protecting cells from free radical damage and by preventing or slowing tumor growth. However, clinical trials have not shown that selenium supplementation -- either alone or combined with other antioxidants -- reduces cancer risk.
Selenium and Heart Disease
In population studies, low antioxidant intake has been associated with increased risk of heart disease. As an antioxidant, selenium may help limit oxidation of "bad" LDL cholesterol, which promotes the build-up of plaque in coronary arteries. However, the "New England Journal of Medicine" reported that selenium supplementation in people with heart disease did not reduce heart disease progression or heart attack risk.
Selenium and Arthritis
According to the Office of Dietary Supplements, dietary surveys have shown that some individuals with arthritis have low selenium intake and low blood levels. It is theorized that selenium may help relieve arthritis symptoms by controlling levels of free radicals. Further research is needed to prove the benefits of selenium supplementation.
Selenium and HIV
In HIV and AIDS, malabsorption can lead to selenium deficiency, which is associated with decreased immune cell counts, increased disease progression and high risk of death. Research results have been contradictory so routine selenium supplementation is not recommended unless selenium levels are low. Individuals with HIV should aim to meet the RDA for selenium.
Side Effects
The Institute of Medicine has set the upper limit for selenium at 400 μg daily. Too much selenium is rare but can lead to selenosis, a condition causing nausea, vomiting, hair loss, white streaking on nails, garlic breath odor, fatigue, irritability and mild nerve damage. Long-term use of selenium supplements may increase risk of Type 2 diabetes and skin cancer recurrence. Selenium supplementation can reduce fertility in men and worsen hypothyroidism. Stop taking selenium at least two weeks before and after surgery, as it may increase risk of bleeding. Selenium supplements may interact with anticoagulants, cholesterol-lowering medications and barbiturates.
